The present invention relates to improvements to gas burners for cookers, comprising a burner head bounded by an approximately frustoconical peripheral side wall with a small cross section located at the top and including a multiplicity of slots distributed peripherally and forming flame orifices, the said burner head being topped by a cover or cap.
In FIG. 1 of the appended drawings, a conventional gas burner arrangement for a cooker has been shown highly schematically. This gas burner essentially comprises, and only as regards the invention, a burner head 1 bounded by a peripheral side wall 2. This peripheral wall 2 is slightly frustoconical with its small cross section located at the top. The peripheral wall 2 is provided with a multiplicity of slots 3, with an approximately horizontal bottom 8, these being distributed peripherally and forming orifices for flames 4. The burner head 1 is topped by a removable cover or cap 5, which closes off the top of the slots 3 and defines the flame orifices.
As regards the rest of the gas burner, this may be constructed in any appropriate manner; in particular, for extra-flat burners, the burner may, in a manner known per se, include a radial annular venturi defined by the lower face of the cap 5.
In currently known gas burners, the side wall 2 of the burner head is inclined only very slightly to the vertical, this angle of inclination typically not exceeding 1 to 3xc2x0. As a result, the flames 4, which leave their respective orifices 3 approximately perpendicular to this wall 2, have a tendency to move substantially away from the wall of the burner head and come into contact with the bottom 6 of a vessel 7 of suitable dimensions for the burner only in the vicinity of the peripheral edge of the said bottom of the vessel, as may be clearly seen in FIG. 1. Under these conditions, the bottom of the vessel is heated less in its central region: the vessel is not heated substantially homogeneously over its entire surface, while an appreciable fraction of the heat escapes to the side and is lost.
The invention aims to provide an improved arrangement which, for a given burner diameter, leads to an appreciably higher burner efficiency and a substantially increased heating rate, without it also resulting in any complication in the structure of the manufacture of the burner.
For these purposes, a gas burner as mentioned in the preamble is characterized, being designed in accordance with the invention, in that the side wall has an angle of inclination to the vertical of 10 to 20xc2x0, advantageously about 15xc2x0, and in that the bottom of each slot forming a flame orifice, which extends transversely to said side wall, has an angle of inclination to the horizontal of 20xc2x0 to 30xc2x0, advantageously about 25xc2x0.
By virtue of this arrangement, the flames leave the respective orifices closer to the vertical so that they reach the bottom of the vessel in a more central region thereof and this bottom is heated more homogeneously. Correspondingly, a smaller fraction of the heat escapes to the side. In total, the heat is transmitted to the vessel and to its contents under appreciably better conditions and the overall efficiency of the burner is substantially improved.
In a standard gas burner arrangement in which the cap projects radially outwards beyond the side wall of the burner head, provision is made, in accordance with the invention, for the peripheral annular portion of the lower face of the cap, which projects radially beyond the side wall of the burner head, to be inclined by approximately 90xc2x0 to 110xc2x0, preferably around 100xc2x0, and to have a stand-off with respect to the said side wall; thus, the shape given to the projecting portion of the cap is more clear of the space above the flame orifices and allows the flames to stand up better.
Again for the same purpose, and optionally in combination with the arrangements that have just been explained, provision may be made for the peripheral annular portion of the lower face of the cap, which projects radially beyond the side wall of the burner head, to have a stand-off of about 2 mm to 6 mm with respect to the bearing surface of the cap on the top of the burner head; advantageously, the stand-off is about 3 mm. Such an arrangement has the advantage of being structurally simple and easy to manufacture.
The implementation of the arrangements of the invention results in a shorter heating time, for example to bring a given volume of liquid to boiling. To be more specific, to bring a 6 liter volume of water, contained in a vessel having a diameter of 203 mm, from a temperature of 22xc2x0 C. to a temperature of 98xc2x0 C., a time of around 21 min is required with a burner designed in accordance with the invention, as opposed to about 25 min with a conventionally designed burner. The arrangements according to the invention therefore allow the heating time to be substantially reduced (by around 16% in the example in question) and therefore result in a corresponding saving in gas consumption.